The objectives of this work are 1) to continue exploration of the role of cellular physical properties as determinants of release of maturing myeloid and erythroid elements from the bone marrow, 2) to study cellular physical properties as determinants of red and white cell lifespan within the circulation in hemolytic anemia and in leukemia, 3) to relate cell physical properties to cellular contractile protein and the latter to ATP, Ca, Mg and Zn balance within cells. 4) to study marrow and spleen ultrastructure in human leukemia (CML) and myeloid metaplasia as well as Mg-deficiency-associated rat leukemia. Studies of cell physical properties will include deformability measurements (micropipette and filterability), electrophoreses, cell adhesion, motility, viscosity and phagocytic measurements. Electron microscopic studies will be made on bone marrow and spleen of normal and leukemic animals and humans.